Mordant dye, colorant that can be bound to a material for which it otherwise has little or no affinity by the addition of a mordant, a chemical that combines with the dye and the fibre. As the principal modern mordants are dichromates and chromium complexes, mordant dye usually means chrome dye. Most mordant dyes yield different colours with different mordants. Mordant dyes can be used with wool, wool blends, silk, cotton, and certain modified-cellulose fibres.

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...dyes include acid dyes, used mainly for dyeing wool, silk, and nylon; and direct or substantive dyes, which have a strong affinity for cellulose fibres (see table). Mordant dyes require the addition of chemical substances, such as salts, to give them an affinity for the material being dyed. They are applied to cellulosic fibres, wool, or silk after such...

Highly skilled craftsmen with closely guarded secret formulas rendered dyeing a well-protected trade. The formation of different colours by mixing red, blue, and yellow dyes was well known in ancient times, as was the use of metal salts to aid the retention of dyes on the desired material and to vary the resultant colours. Natural dyes cannot be applied directly to cotton, in contrast to wool...

In several mordant dyes, the anthraquinone structure contains hydroxyl groups that participate in binding the dye to fibres such as cotton, wool, or silk that have been previously impregnated with the oxide of a metal such as aluminum, iron, tin, or chromium.